1. Field of the Invention
This invention relates to a radiation image recording medium, which is capable of recording a radiation image when it is exposed to radiation carrying image information, and which comprises a plurality of transparent linear electrodes for reading of an electric charge signal formed in accordance with the recorded radiation image. This invention also relates to an image displaying medium, which is capable of displaying image information in accordance with an alteration in optical characteristics caused to occur by voltage application performed in accordance with the image information, and which comprises a plurality of transparent linear electrodes to be applied with the voltage in accordance with the image information.
2. Description of the Related Art
Various radiation image recording media, which are capable of generating electric charges when being exposed to radiation carrying image information of an object, and which are capable of recording a radiation image of the object through accumulation of the electric charges, have heretofore been proposed and used in practice in medical fields, and the like.
As one of the radiation image recording media described above, there has been proposed a radiation image recording medium, comprising:
i) a first electrode layer, which has transmissivity to radiation,
ii) a recording photo-conductor layer, which generates electric charges when it is exposed to the radiation,
iii) a charge transporting layer, which acts as an insulator with respect to electric charges having a certain polarity, and which acts as a conductor with respect to electric charges having an opposite polarity,
iv) a reading photo-conductor layer, which generates electric charges when it is exposed to reading light, and
v) a second electrode layer, which is constituted of transparent linear electrodes having transmissivity to the reading light and reading light non-transmissive linear electrodes for blocking the reading light, the transparent linear electrodes and the reading light non-transmissive linear electrodes being arrayed alternately and in parallel,
the layers being overlaid in this order.
The proposed radiation image recording medium is described in, for example, U.S. Pat. No. 6,770,901.
FIGS. 7A, 7B, and 7C are explanatory views showing how a conventional radiation image recording medium operates. As illustrated in FIG. 7A, in cases where a radiation image is to be recorded with the radiation image recording medium having the constitution described above, a negative high voltage is applied to a first electrode layer 1 of the radiation image recording medium from a high voltage electric power source, which is connected to the first electrode layer 1. Also, in this state, radiation carrying image information of an object is irradiated to the first electrode layer 1. The radiation, which has been irradiated to the first electrode layer 1, passes through the first electrode layer 1 and impinges upon a recording photo-conductor layer 2. As a result, pairs of positive and negative charges are generated at an area of the recording photo-conductor layer 2, which area has been exposed to the radiation. Of the pairs of positive and negative charges having been generated in the recording photo-conductor layer 2, the positive charges move toward the first electrode layer 1, which has been charged negatively. The positive charges, which have thus moved toward the first electrode layer 1, combine with the negative charges of the first electrode layer 1 and disappear. Of the pairs of positive and negative charges having been generated in the recording photo-conductor layer 2, the negative charges move toward a second electrode layer 5, which has been charged positively. A charge transporting layer 3 acts as the insulator with respect to the negative charges. Therefore, as illustrated in FIG. 7B, the negative charges, which thus move within the recording photo-conductor layer 2 and toward the second electrode layer 5, are accumulated at a charge accumulating section 6, which is an interface between the recording photo-conductor layer 2 and the charge transporting layer 3. The recording of the radiation image is performed through the accumulation of the negative charges at the charge accumulating section 6.
As illustrated in FIG. 7C, in cases where the radiation image having thus been recorded is to be read out from the radiation image recording medium, the reading light is irradiated to the radiation image recording medium from the side of the second electrode layer 5. The reading light, which has been irradiated to the second electrode layer 5, passes through a transparent linear electrode 5a of the second electrode layer 5 and impinges upon a reading photo-conductor layer 4. As a result, pairs of positive and negative charges are generated in the reading photo-conductor layer 4. Of the pairs of positive and negative charges having been generated in the reading photo-conductor layer 4, the positive charges combine with the negative charges, which have been accumulated at the charge accumulating section 6. Also, of the pairs of positive and negative charges having been generated in the reading photo-conductor layer 4, the negative charges combine with the positive charges of the transparent linear electrode 5a and the positive charges, which flow from a reading light non-transmissive electrode 5b toward the side of the transparent linear electrode 5a via the ground. An electric current i caused to occur in this manner is detected by a current detecting amplifier 8, which is connected to the transparent linear electrode 5a. The electric current i is converted into a voltage, and an image signal is thus acquired.
By way of example, a radiation image of a mamma may be recorded by use of the radiation image recording medium described above, the recorded radiation image of the mamma may then be read out from the radiation image recording medium, and an image signal representing the radiation image of the mamma may thereby be acquired. In such cases, it is necessary for a width of each of pixels constituting the radiation image to be set at approximately 50 μm. Therefore, it is necessary for the width of each of the transparent linear electrodes to be set at approximately 10 μm to 20 μm. However, in cases where the thin transparent linear electrode is formed, since the material for the transparent linear electrode is an oxide material, such as indium tin oxide (ITO), which has a high specific resistance, the line resistance of the transparent linear electrode becomes high. Therefore, thermal noise at the current detecting amplifier becomes high, and the signal-to-noise ratio of the acquired image signal becomes low. Also, in cases where the line resistance of the transparent linear electrode is high, a time constant at the time of the acquisition of the image signal becomes long, and the response speed becomes low. As a technique for reducing the line resistance of the transparent linear electrode, there has been proposed a technique, wherein an opaque electrically-conductive member made from, for example, a metal having an electrical conductivity higher than the electrical conductivity of the transparent linear electrode, is located such that the opaque electrically-conductive member is in contact with the transparent linear electrode. The proposed technique for reducing the line resistance of the transparent linear electrode is described in, for example, Japanese Unexamined Patent Publication No. 2001-284565.
However, with the radiation image recording medium described in, for example, Japanese Unexamined Patent Publication No. 2001-284565, the opaque electrically-conductive member is located on a top surface of an end region of the transparent linear electrode, which end region extends along the longitudinal direction of the transparent linear electrode. Therefore, the reading light, which impinges upon the end region of the transparent linear electrode, is blocked by the opaque electrically-conductive member, and the electric charges are not capable of being generated at an area of the reading photo-conductor layer, which area is located in the vicinity of the end region of the transparent linear electrode. In cases where the radiation image readout is performed by the utilization of the transparent linear electrodes and the reading light non-transmissive electrodes as in the cases of the radiation image recording medium described in, for example, U.S. Pat. No. 6,770,901, generation of the electric charges at the area in the vicinity of the end region of each of the transparent linear electrodes contributes markedly to an efficiency, with which the image signal is read out. Therefore, in such cases, if the opaque electrically-conductive member is located on the top surface of the end region of the transparent linear electrode as in the cases of the radiation image recording medium described in, for example, Japanese Unexamined Patent Publication No. 2001-284565, an image signal having a sufficient level will not be capable of being acquired, and the signal-to-noise ratio of the acquired image signal will not be capable of being kept high.
As described above, in the cases of the radiation image recording medium described in, for example, U.S. Pat. No. 6,770,901, the radiation image readout is performed by the utilization of the transparent linear electrodes and the reading light non-transmissive electrodes. Besides the radiation image recording medium described in, for example, U.S. Pat. No. 6,770,901, there has also been proposed a radiation image recording medium, wherein the radiation image readout is performed by the utilization of the transparent linear electrodes alone. In the cases of the proposed radiation image recording medium, wherein the radiation image readout is performed by the utilization of the transparent linear electrodes alone, in order for noise at the current detecting amplifier to be reduced, it is necessary that the inter-neighbor capacity between the adjacent transparent linear electrodes be kept as small as possible. Therefore, it is desired that the ratio of the width of each of the transparent linear electrodes to the array pitch of the transparent linear electrodes is capable of being kept as low as possible. However, such that the ratio of the width of each of the transparent linear electrodes to the array pitch of the transparent linear electrodes may be kept as low as possible, and such that the line resistance of each of the transparent linear electrodes may be kept low, if the opaque electrically-conductive member is located on the top surface of the end region of the transparent linear electrode as in the cases of the radiation image recording medium described in, for example, Japanese Unexamined Patent Publication No. 2001-284565, the efficiency, with which the image signal is read out, will not be capable of being kept high.
Further, besides the radiation image recording media described above, an image displaying medium utilizing the transparent linear electrodes has been proposed in, for example, Japanese Patent Application No. 2003-433467. The proposed image displaying medium comprises:
i) a displaying layer, whose optical characteristics alter in accordance with an applied electric field,
ii) an optical switching layer, which is capable of generating electric charges for the formation of the electric field when being exposed to an address light for displaying, and
iii) an electrode layer, which is provided with a plurality of transparent linear electrodes arrayed in parallel with one another, the transparent linear electrodes being capable of transmitting the address light for displaying,
the displaying layer, the optical switching layer, and the electrode layer being overlaid in this order.
The proposed image displaying medium is operated in the manner described below. Specifically, a voltage in accordance with image information is applied selectively to each of the transparent linear electrodes of the electrode layer. Also, the address light, which extends in a direction normal to the longitudinal direction of each of the transparent linear electrodes, is caused to scan from the side of the electrode layer and along the longitudinal direction of each of the transparent linear electrodes. With the irradiation of the address light, electric charges are caused to occur in the optical switching layer. An electric field is formed in the displaying layer by the electric charges occurring in the optical switching layer. The optical characteristics of the displaying layer alters in accordance with the electric field, and the image information is thereby displayed.
In the cases of the proposed image displaying medium, in order for quick image displaying to be enabled, it is necessary that the inter-neighbor capacity between the adjacent transparent linear electrodes be kept as small as possible, and that the time constant be kept as short as possible. Therefore, it is desired that the ratio of the width of each of the transparent linear electrodes to the array pitch of the transparent linear electrodes is capable of being kept as low as possible. However, in cases where the ratio of the width of each of the transparent linear electrodes to the array pitch of the transparent linear electrodes is set to be low, the area of each of the transparent linear electrodes, which area contributes to the generation of the electric charges in the optical switching layer, becomes small. Accordingly, a region, at which the image information is not displayed appropriately, occurs in the range of the area of the displaying layer, which range corresponds to the area between the adjacent transparent linear electrodes. Also, quick image displaying may be enabled with the technique, in which the opaque electrically-conductive member is located on the top surface of the end region of the transparent linear electrode as in the cases of the radiation image recording medium described in, for example, Japanese Unexamined Patent Publication No. 2001-284565, such that the line resistance may be kept low and such that the time constant may be kept short. However, if the opaque electrically-conductive member is located on the top surface of the end region of the transparent linear electrode as in the cases of the radiation image recording medium described in, for example, Japanese Unexamined Patent Publication No. 2001-284565, since the electric charges are not capable of being generated at the area of the optical switching layer, which area is located in the vicinity of the end region of the transparent linear electrode, a region, at which the image information is not displayed appropriately, will occur in the range of the area of the displaying layer, which range corresponds to the area between the adjacent transparent linear electrodes.